Several processes may be used in the cleaning of waste water, depending on the type and the contaminants. One such technology is membrane treatment, which may be used for removal of dissolved species, organic compounds, human pathogens etc.
Membrane filtration is a physical separation process and the driving force is the pressure difference across the membrane. By using different membrane types, molecules of varying sizes may be separated. Membrane filtration may be used for microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO).
Membrane technologies is used in so called membrane bioreactors (MBRs), in which membranes e.g. are immersed in a tank (bioreactor) comprising the waste water to be treated. One consideration in MBR-technology is fouling of the membranes. Fouling is the result of interaction between the membrane and components of the waste water such as dead microorganism and soluble and/or colloidal compounds. Therefore, several MBRs are operated under cross-flow conditions, in which there is a flow of filtrate over the membrane in order to avoid build-up of solids on the membrane surface. This increases the performance of the membrane and increases the plant capacity.
A membrane bioreactor often includes several membranes in order to have as large membrane surface as possible. Membranes are usually attached to some sort of support, and water having passed the membrane (permeate) is led out from the MBR.
U.S. Pat. No. 7,678,273 discloses a filter unit comprising several membrane plates that are welded together at a small welding zone, manly for preventing leakage of concentrate to permeate in the unit.
US 2010/0096317 discloses a flat sheet membrane element for performing solid-liquid separation by immersion in a liquid. Collected permeate within the support plates for the filtration membranes is guided in a direction parallel to the direction of the liquid that is to be filtrated.
U.S. Pat. No. 5,482,625 discloses a filtration membrane module comprising several membrane supporting plates. The membrane supporting plate itself is manufactured by some sort of click-system to form permeate channels within the plate.
There is however a need in the art for improved and simplified methods of producing membrane units for a membrane bioreactor.